The invention relates to a pressure mediator for transmitting a pressure of a pressure prevailing in a first medium to a second medium.
More precisely, the invention relates to a pressure mediator having a base body; a divider diaphragm system having a first divider diaphragm and a second divider diaphragm, between which an intermediate chamber is enclosed in pressuretight fashion, in which the first surface of the first divider diaphragm, remote from the intermediate chamber, can be acted upon by the pressure prevailing in the first medium, and the first surface of the second divider diaphragm, remote from the intermediate chamber, is oriented toward the base body and with the base body forms a pressure chamber, which can be filled with the second medium and has a pressure chamber opening, through which the pressure can be transmitted by means of the second medium, and an exertion of pressure of the first divider diaphragm can also be transmitted to the second divider diaphragm via the intermediate volume; and having a sensor, for monitoring a property of the intermediate chamber.
Among other uses, pressure mediators are used in measuring pressure in aggressive media; the divider diaphragm is subjected to an aggressive first medium, and the pressure prevailing in the first medium is transmitted to a second medium in the pressure chamber, from where it is delivered to a pressure measuring cell via a suitable pressure supply line. A pressure transmission with a pressure mediator and a pressure line connected to it can, however, also be desired with nonaggressive media, in order to span long distances between the first medium and the site of the pressure measuring cell, or in order to keep a pressure measuring cell far away from the high temperatures of the first medium.
For pressure transmission, incompressible oils are preferably used as the second medium. To the extent that such a medium is capable of contaminating a measurement medium, and for various other reasons, it is necessary for a leak or break in the divider diaphragm or a divider diaphragm system to be detected early.
To this end, Wiegand et al., in German Patent Disclosure DE 199 49 831A1, disclose a generic pressure mediator in which the first diaphragm and the second diaphragm have the same design, and the intermediate chamber is evacuated. The sensor for monitoring a property of the intermediate chamber is a simple pressure sensor, which detects a leak in the diaphragm system from a change in pressure in the intermediate chamber.
In the unpublished German Patent Application 101 44230.0 of Bernauer et al, a pressure measuring instrument with a generic pressure mediator is disclosed in which the intermediate chamber between the first diaphragm and the second diaphragm is filled with a liquid or a solid. A leak in the diaphragm system can then be detected for instance from a change in the consistency of the liquid or from the penetration of the first or second medium into the intermediate chamber, on the basis of a change in the dielectric properties, the conductivity, or the optimal properties, by means of a suitable sensor. The arrangement of Bernauer et al. is advantageous in the sense that less-pronounced hysteresis effects are expected than in the diaphragm system of the teaching of Wiegand et al., because the forces of friction between the corrugated diaphragms resting directly on one another should be greater than the forces of gravity that occur between diaphragms spaced apart from one another in the event of deflections. This is particularly the case if the intermediate chamber is filled with liquid.
The devices described above meet the purpose of being capable of detecting a diaphragm break, but the equipment described above requires complete retrofitting of the measurement sites already in operation. Furthermore, the many kinds of pressure measuring applications would require a large number of different pressure mediators with the diaphragm systems described, with two divider diaphragms, in order to suitably meet existing conditions. This means a very high production cost.
It is therefore the object of the present invention to furnish a pressure mediator of this generic type which overcomes the described disadvantages of the prior art.
This object is attained according to the invention by a pressure mediator including: a base body; a divider diaphragm system having a first divider diaphragm and a second divider diaphragm, between which an intermediate chamber is enclosed in pressuretight fashion, in which the first surface of the first divider diaphragm, remote from the intermediate chamber, can be acted upon by the pressure prevailing in the first medium, and the first surface of the second divider diaphragm, remote from the intermediate chamber, is oriented toward the base body and is secured by its peripheral region to the base body, forming a pressure chamber between the base body and the second divider diaphragm, and the pressure chamber can be filled with the second medium and has a pressure chamber opening, though which the pressure can be transmitted by means of the second medium, and an exertion of pressure of the first divider diaphragm can also be transmitted to the second divider diaphragm via the intermediate volume; and having a sensor, for monitoring a property of the intermediate chamber, characterized in that the pressure mediator furthermore has a diaphragm module, which includes a pressure chamber, to which the first divider diaphragm is secured by its peripheral region, and the diaphragm module is secured to the base body by means of the module body.
The sensor for monitoring a property of the intermediate chamber can be disposed both on the base body and on the diaphragm module.
Particularly in diaphragm modules for retrofitting pressure mediators without monitoring for broken diaphragms, the sensor for monitoring a property of the intermediate chamber is preferably disposed on the diaphragm module. In a modular version of pressure mediators of the invention, the sensor can be disposed both on the base body and on the sensor module; mounting the sensor on the base body is currently preferred at least whenever the pressure mediator is a component of a pressure measuring instrument or differential pressure measuring instrument with a pressure measuring cell, since in that case the requisite connections of the sensor can easily be extended into the electronics housing of the pressure measuring instrument.
As detection principles, all the principles named above for monitoring broken diaphragms can be employed; at present, a capacitive or conductive monitoring of a liquid in the intermediate chamber is preferred.
For diaphragm modules for retrofitting on pressure mediators with a process connection, it is recommended that the diaphragm module, on its side toward the pressure mediator, have a connection that is complementary to the process connection, and a corresponding process connection on the side toward the process. In new construction of pressure mediators of the invention, modules with different process connections can be secured to the base body via a uniform module connection.
In terms of the embodiment of the diaphragm modules, these may among other have a diaphragm bed for the first divider diaphragm and optionally a separate overload mechanism.
The first divider diaphragm can have the same geometric dimensions as the second divider diaphragm, but in principle other dimensions are also possible. For reducing the overall rigidity of the divider diaphragm system, the second divider diaphragm can have a considerably thinner material thickness as well as more-favorable materials than the first divider diaphragm, since the second divider diaphragm no longer comes into contact with corrosive media.
If the geometric conditions allow this, the second divider diaphragm can have a larger diameter than the first divider diaphragm, so that for a given material thickness, the diaphragm forces for the requisite lifting volume of the diaphragm can be minimized.
The diaphragm module should preferably be detachably connected to the base body, so that it can be replaced easily after a diaphragm has broken.